1. Field of the Invention
This invention relates to an improved system and method of cleansing a filter bed. In particular, this invention relates to an automatic backwash filtering system. Further, this invention directs itself to an improved system for cleansing a filter bed utilizing two separate and distinct operation cycles, including a backwashing cycle and a purge cycle. Additionally, this invention relates to an automatic backwashing filter system which permits substantial utilization of identical fluid flow elements in both a backwashing operation and a purge operation. Still further, this invention relates to an automatic backwashing filter system wherein standard backwash pumps may be utilized by appropriate throttling techniques in both the backwash cycle and the purge cycle.
2. Prior Art
Automatic backwash filter systems are known in the art as exemplified in U.S. Pat. Nos. #3,239,061 and #4,133,766, assigned to the Assignee Corporation of this invention concept. However, such automatic backwash filters provide for a singular backwashing operation of the filter beds. It has been found in such prior art systems that there is a possibility that particulate solid contaminants or organisms have been found at the bottom of the filter bed subsequent to the backwashing operation. In such prior art systems, there is a possibility that the particulate material may pass through the filter underdrain and contaminate the filtrate. Additionally, such prior art systems do not purge the filter bed subsequent to the backwashing operation cycle for removal of further contaminants from the filter bed. Thus, in such prior art filtering systems, the safety factor does not provide for a maximization of the filtering of the overall filtering system.
Additionally, where it would be necessary to insert a purge cycle into the prior art filtering systems, such would be overly complicated by additional hardware and pumping consideration mechanisms which would increase the cost of such systems. Still further, additional hardware and pumping elements applied to prior art systems for the purge cycle would unnecessarily increase the volume considerations for such filtering systems.